Neutron Moderation Theory Taking into Accout the Thermal Motion of Moderating Medium Nuclei

In this paper we present the analytical expression for the neutron scattering law for an isotropic source of neutrons, obtained within the framework of the gas model with the temperature of the moderating medium as a parameter. The obtained scattering law is based on the solution of the kinematic problem of elastic scattering of neutrons on nuclei in the L-system in the general case. I.e. both the neutron and the nucleus possess the arbitrary velocity vectors in the L-system. For the new scattering law the flux densities and neutron moderation spectra depending on the temperature are obtained for the reactor fissile medium. The expressions for the moderating neutrons spectra allow reinterpreting the physical nature of the underlying processes in the thermal region.Comment: 26 pages, 6 figure

Ultraslow Wave Nuclear Burning of Uranium-Plutonium Fissile Medium on Epithermal Neutrons

For a fissile medium, originally consisting of uranium-238, the investigation of fulfillment of the wave burning criterion in a wide range of neutron energies is conducted for the first time, and a possibility of wave nuclear burning not only in the region of fast neutrons, but also for cold, epithermal and resonance ones is discovered for the first time. For the first time the results of the investigation of the Feoktistov criterion fulfillment for a fissile medium, originally consisting of uranium-238 dioxide with enrichments 4.38%, 2.00%, 1.00%, 0.71% and 0.50% with respect to uranium-235, in the region of neutron energies 0.015-10.0eV are presented. These results indicate a possibility of ultraslow wave neutron-nuclear burning mode realization in the uranium-plutonium media, originally (before the wave initiation by external neutron source) having enrichments with respect to uranium-235, corresponding to the subcritical state, in the regions of cold, thermal, epithermal and resonance neutrons. In order to validate the conclusions, based on the slow wave neutron-nuclear burning criterion fulfillment depending on the neutron energy, the numerical modeling of ultraslow wave neutron-nuclear burning of a natural uranium in the epithermal region of neutron energies (0.1-7.0eV) was conducted for the first time. The presented simulated results indicate the realization of the ultraslow wave neutron-nuclear burning of the natural uranium for the epithermal neutrons.Comment: 35 pages, 19 figures (v2: Fig12 and some misprints in the text are fixed

Fukushima plutonium effect and blow-up regimes in neutron-multiplying media

It is shown that the capture and fission cross-sections of 238U and 239Pu increase with temperature within 1000-3000 K range, in contrast to those of 235U, that under certain conditions may lead to the so-called blow-up modes, stimulating the anomalous neutron flux and nuclear fuel temperature growth. Some features of the blow-up regimes in neutron-multiplying media are discussed.Comment: 15 pages, 8 figures. (v2: numerous corrections and style improvements). arXiv admin note: substantial text overlap with arXiv:1207.369

Orbital forcings of the Earth?s climate in wavelet domain

International audienceWe examine two paleoclimate proxy records ? the temperature differences from the Antarctic Vostok ice core and the composite ?18O record from three sites (V19-30, ODP 677, and ODP 846) ? in order to search for indications of orbital forcings. We demonstrate that the non-decimated wavelet transform is an appropriate tool for investigating temporarily changing spectral properties of records. Our results indicate that abrupt climate warmings with cyclicity of ~100 kiloyears during the last 400 kiloyears were caused by the combined unidirectional influences of three orbital parameters and the eccentricity can be considered as a modulator defining transitions from the Ice Ages to the periods of comparative warmings. Non-decimated wavelet transform avails discovering the possible part played in climate change by the eccentricity-forced variations. Up to approximately 1.7 million years BP, the influence of this variations of eccentricity appears in increasing for almost all local maxima of ?18O. Since the ~1.7 million years BP, minor and significant maxima alternated and this not affected as much the variations of ?18O